Based on the provided code slice and the identified vulnerability (CWE-476: NULL Pointer Dereference) on line 14, here are five possible patches to address the issue:

Patch 1:
```c
if (dir && !IS_ERR(dir)) {
    simple_recursive_removal(dir, NULL);
    dput(dir);
} else {
    pr_err("Invalid directory entry for unit %s\n", unit);
}
```

Patch 2:
```c
if (!IS_ERR_OR_NULL(dir)) {
    simple_recursive_removal(dir, NULL);
    dput(dir);
} else {
    pr_err("Failed to get valid directory entry for unit %s\n", unit);
}
```

Patch 3:
```c
struct dentry *valid_dir = dget(dir);
if (valid_dir) {
    simple_recursive_removal(valid_dir, NULL);
    dput(valid_dir);
} else {
    pr_err("Unable to get reference to directory for unit %s\n", unit);
}
```

Patch 4:
```c
if (d_is_dir(dir)) {
    simple_recursive_removal(dir, NULL);
    dput(dir);
} else {
    pr_err("Entry for unit %s is not a directory\n", unit);
    dput(dir);
}
```

Patch 5:
```c
if (dir && d_really_is_positive(dir)) {
    simple_recursive_removal(dir, NULL);
    dput(dir);
} else {
    pr_err("Invalid or negative dentry for unit %s\n", unit);
    if (dir)
        dput(dir);
}
```

Each of these patches aims to check the validity of the `dir` pointer before calling `simple_recursive_removal()`, and properly handle the case where `dir` might be NULL or an error value. They also include proper cleanup (using `dput()`) to avoid potential resource leaks.